ABSTRACT
This research is conducted to assess the accuracy of spline interpolation methods to predict and
model the surface water pH of Pulau Tuba, Langkawi, Kedah, Malaysia. In-situ sampling
activities using pH-meter and Geographic Positioning Systems (GPS) were carried out during
high tides and at noon in November 2018. The development of spatial models was constructed
using Regularized and Tension spline methods. Then, validation of models was carried out to
compare the observed and predicted values of pH using correlation analysis, regression analysis,
and error analysis. The accuracy of the developed map was calculated using the overall accuracy
equation. This research found that the regularized spline method had more accuracy in estimating
surface water pH variability than the tension spline method. Pearson correlation coefficient (r),
Coefficient of determination (R2
), Mean Absolute Error (MAE) and Root Mean Square Error
(RMSE) were reported at 0.896, 0.803, 0.0265 and 0.0344 for the regularized spline method,
respectively. The developed spatial model was then transformed into a map by adding map
elements such as legend, title, north arrow, and scales for effective visualization. The developed
map has an accuracy of 87.50%. The surface water pH was found at the range of 7-8. Low
reading of pH is expected due to the addition of rainwater to the coastal water of Pulau Tuba,
Langkawi, Kedah. The research outcomes would benefit government and non-government
agencies to monitor the coastal and ocean acidification and the development of strategic policies
and rules to reduce the impact of anthropogenic activities and climate changes for this area.